Reconfigurable devices are devices containing one or several parts that can be actively controlled by means of a signal (electrical, optical or of other nature) to modify the optical response for wave front control of amplitude, phase and/or polarization of electromagnetic waves. Reconfigurable devices may include spatial light modulators (SLM). An example of a simple design for manipulation of amplitude is an arrangement including arrays of micro-mirrors that are able to rotate to switch between reflecting and not reflecting the electromagnetic waves. FIG. 1A is a schematic illustrating a micro-electro-mechanical systems (MEMS) based micro-mirror 100a. FIG. 1B is a schematic illustrating another micro-electro-mechanical systems (MEMS) based micro-mirror 100b. FIG. 1C is a scanning electron microscopy (SEM) image 100c showing a top planar view of a micro-mirror. FIG. 1D is a scanning electron microscopy (SEM) image 100d showing a perspective view of a micro-mirror.
Another way for controlling the phase of electromagnetic waves is realized using an array of cells containing a liquid crystal (LC). A voltage is applied to each individual cell to modify the orientation of the particles comprised in the LC, thus changing the refractive index of the LC. FIG. 2A is a schematic showing a liquid crystal display (LCD) 200a. A LCD may be, for example, a liquid crystal on silicon (LCoS) display or a ferroelectric liquid crystal (FLCoS) in silicon display. FIG. 2B is a schematic showing another liquid crystal display (LCD) 200b. FIG. 2C is a scanning electron microscopy (SEM) image 200c of a liquid crystal display (LCD). A LCD may be, for example, a liquid crystal on silicon (LCoS) display or a ferroelectric liquid crystal (FLCoS) in silicon display. By varying the refractive index of the LC, the electromagnetic waves experience a different optical path in each cell and thus have different phase shifts. For reflection devices, the cell may need to have a sufficient thickness so that an electromagnetic wave passing through the cell experiences at least about half a wavelength shift due to the change in refractive index. Alternatively, for transmission devices, the cell may be required to have a sufficient thickness of at least one wavelength shift due to the change in refractive index. As a consequence of the large thickness, the voltage required to re-orientate the liquid crystal may be rather high. At high voltages, the cross-talk between neighbouring cells or pixels may happen when the cell size is reduced beyond a certain limit. Accordingly, minimum pixel size of the device may also be limited. Currently, commercially available devices may have minimum pixel sizes of around 3 μm, which may impose a serious limitation in the resolution of near-eye devices using liquid crystal technology.